The present invention relates to a fluid jet printing system and particularly relates to apparatus and methods for effecting fluid jet printing serially on one or both sides of a substrate and for minimizing or eliminating shorts in the electrodes of the fluid jet printheads.
Generally, in fluid jet printing, a printhead having a manifold provides fluid, e.g., ink, dye or other chemicals, to an orifice plate through which the fluid issues as a plurality of filaments which break up and form droplet streams. By locating charge electrodes adjacent the filaments, droplets formed from the filaments may be selectively and individually charged. By passing the charged and uncharged droplets through an electrostatic field generated by a deflection electrode, the charged droplets are deflected from a normal downward path toward and onto a collector for recycling back to the manifold. The uncharged droplets are not deflected and therefore fall downwardly on a substrate below the orifice plate. Thus, by selectively charging the droplets, in accordance with a predetermined information signal, pattern printing on a substrate may be effected.
For one-sided application of the fluid to the substrate, it has been found desirable to provide two or more printing stations arranged in series to enable printing operations to be shifted from one printhead to another without stopping the continuous movement of the substrate, e.g., fabric, through the printing stations, to enable servicing of the non-used printhead, and to permit serial application of different printing fluids, i.e., different colors and chemicals. In accordance with the present invention, the rolls carrying the substrate past the printhead at each printing station may be shifted between an operating position lying below the substrate on opposite sides of the printhead whereby the droplet streams deposit fluid on the substrate between the pair of rollers, to an out-of-the-way or inoperative position laterally to one side of the printhead. In this latter position, the printhead of that station may be serviced while the fabric is being printed by the printhead of the other station. Additionally, by using two or more fluid jet printing apparatus in series, two or more different chemicals or dyes may be readily applied to the substrate.
Further, because printheads are inherently capable of printing irrespective of the direction of travel of the substrate thereunder, the substrate, in accordance with the present invention, can be routed through a first fluid jet printing station with a first side up for printing thereon and then routed to travel in the opposite relative direction past the printhead of a second fluid jet printing station with its second side up. Thus, opposite sides of the substrate are sequentially printed, that is to say, a two-sided lash-up or threading configuration enables two-sided printing using two successive printing stations.
Furthermore, it has been found desirable to maintain the electrodes below the orifice plate and above the substrate at each printing station free of dust and other particulate matter during operation of the fluid jet printing apparatus. Particulate matter, such as lint from a fabric passing below and in close proximity to the electrodes, may be displaced from the fabric into the region of the electrodes and short the electrodes whereby the intended printed pattern may not be generated. In this particular fluid jet printing apparatus, it has been found that there is a greater tendency for particulate matter to pass into the region of the electrodes from the substrate when the substrate passes the printhead in one direction in contrast to passing the substrate in the opposite direction. While this phenomena is not fully understood at this time, it is believed related to the location of the catcher along the underside of the print bar and adjacent the droplet stream. Thus, it has been observed that fewer failures, i.e., shorts, in the electrodes occur upon passing the substrate first below the catcher structure, then past the printhead and deflection electrode rather than in the opposite direction, i.e., first past the deflection electrode and then the printhead and catcher.
According to the present invention, there is provided a fluid jet printing apparatus comprising a frame, an elongated fluid jet printhead carried by the frame for printing on a substrate, a pair of laterally spaced rollers carried by the frame substantially coextensive in length with the printhead for locating the substrate in a first position in opposition to the printhead with the rollers located adjacent opposite sides of the printhead, means carried by the frame for mounting said rollers for movement from the first position into a second position spaced from the printhead and means carried by the frame for moving the rollers from the first position into the second position.
In accordance with another aspect of the present invention, there is provided a fluid jet printing system for printing on a continuous substrate comprising first and second fluid jet printing stations, each printing station comprising fluid jet printing apparatus having an elongated fluid jet printhead including a manifold having a reservoir for fluid, an orifice plate for flowing fluid from the reservoir for printing on the substrate, and a pair of laterally spaced rollers substantially coextensive in length with the printhead for positioning the substrate in opposition to the printhead with the rollers located adjacent opposite sides of the printhead, means for continuously feeding the substrate through the first and second printing apparatus, means carried by one of the first and second apparatus for mounting the pair of rollers associated therewith for movement from a first position thereof in opposition to the printhead into a second position spaced from the printhead and means carried by the one apparatus for moving the associated pairs of rollers from the first position into the second position whereby printing may be effected only by the other of the apparatus.
In a still further aspect of the present invention, there is provided a fluid jet printing apparatus comprising a printhead having an orifice plate and a manifold defining a reservoir for fluids whereby said fluid filaments issue through the orifice plate to form fluid droplets, means mounting a substrate in spaced opposition to and for movement past the orifice plate, the printhead including electrode means disposed below the orifice plate and between the orifice plate and the substrate, including a charge electrode for providing electrostatically charged fluid droplets, a catcher disposed below said orifice plate, the electrode means including a deflection electrode for establishing a field to deflect charged droplets through the catcher whereby uncharged droplets are deposited on the substrate and means for moving the substrate along the mounting means in a direction to first pass the catcher, with subsequent deposition of the uncharged droplets on the substrate, whereby the tendency of particulate matter carried by the substrate to enter to region of the electrodes is minimized or eliminated.
A still further aspect hereof provides a method of operating a fluid jet printing system having a fluid jet printhead including an orifice plate and an electrode structure for selectively depositing fluid droplets onto an underlying substrate carried by a pair of rollers comprising the steps of positioning the pair of rollers below the printhead in a first position in opposition to the orifice plate and on opposite sides thereof for receiving the fluid droplets on the substrate and moving the pair of rollers from the first position to a second position removed from the first position thereof whereby the substrate is removed from its position in opposition to the substrate.
Preferably, a plurality of printing stations are provided, with each station having a printhead of the foregoing type. Printing may therefore be provided on the substrate using different dyes or chemicals and on opposite sides of the substrate.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus and methods for fluid jet printing on a substrate wherein a plurality of fluid jet printing stations comprising a printing system are arranged in series to print a substrate with fluids of different chemicals, dyes, or the like and on one or both sides thereof. The serially arranged fluid jet printing stations enable servicing one or more of the serially arranged printheads while continuously moving the substrate through the printing system, i.e., eliminating system downtime.
It is a further object of the present invention to provide a novel and improved apparatus and methods for minimizing or eliminating shorts in the electrode system of a fluid jet printhead by passing the substrate relative to the printhead in a particular direction relative to the electrode system of the fluid jet printhead.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.